Phosphothreonine as a Catalytic Residue in Peptide-Mediated Asymmetric Transfer Hydrogenations of 8-Aminoquinolines

Phosphothreonine (pThr) was found to constitute a new class of chiral phosphoric acid (CPA) catalyst upon insertion into peptides. To demonstrate the potential of these phosphopeptides as asymmetric catalysts, enantioselective transfer hydrogenations of a previously underexplored substrate class for CPA-catalyzed reductions were carried out. pThr-containing peptides lead to the observation of enantio-selectivities of up to 94:6 e.r. with 2-substituted quinolines containing C8-amino functionality. NMR studies indicate that hydrogen-bonding interactions promote strong complexation between substrates and a rigid beta-turn catalyst.